It may be desirable to reduce engine emissions at time of engine starting so that average engine emissions over a driving cycle may be reduced. One way to improve engine emissions at the time of starting is to operate an engine rich and to supply air to an exhaust system coupled to the engine. Such operation allows engine exhaust gas constituents to be oxidized in the exhaust system. In particular, hydrocarbons in the exhaust gases may be oxidized when combined with air introduced to the exhaust system. The oxidizing hydrocarbons release heat that may be transferred to an after treatment devices in the exhaust system. The heat transfer reduces an amount of time that it takes for the after treatment device to reach operating temperature. Consequently, the after treatment device may begin to convert exhaust constituents to more desirable compounds sooner after engine starting, thereby reducing engine emissions. However, systems that inject air into an engine exhaust system increase system cost and may be less reliable than systems that do not inject air into engine exhaust.
The inventors herein have recognized the above-mentioned limitations and have developed a method for operating an engine, comprising: rotating a turbocharger coupled to the engine in a first direction to increase a time engine exhaust gases are in an exhaust manifold; and rotating the turbocharger in a second direction different than the first direction to increase engine output torque.
By rotating a turbocharger in two different directions, it may be possible to both improve engine emissions and engine power output. For example, after an engine start, a turbocharger may be rotated in a first direction opposed to a direction that engine exhaust gases drive the turbocharger so that exhaust gases experience a greater latency time in the engine exhaust manifold. A greater latency time may allow for more complete oxidation of exhaust gases in the exhaust manifold so that engine emissions may be improved. Additionally, rotating the turbocharger in a first direction opposed to a direction the turbocharger rotates when acted upon by exhaust gases exiting engine cylinders may increase exhaust back pressure which may also help to improve engine emissions during some conditions. Subsequently, the turbocharger may be rotated in a second direction that pressurizes air entering the engine to increase engine performance.
The present description may provide several advantages. In particular, the approach may reduce engine emissions during an engine cold start. Further, the approach may reduce fuel consumption by reducing catalyst light off time so that an amount of time the engine is operated less efficiently may be reduced. Additionally, the approach may provide for a more reliable way to reduce engine emissions as compared to systems that utilize secondary air injection to the exhaust system.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.